1. FIELD OF THE INVENTION
The present invention relates to an automatic transmission used with a torque converter for an automobile, particulary to a multipule speed automatic transmission comprising a main transmission mechanism and a sub transmission mechanism.
2. DESCRIPTION OF THE PRIOR ART
An automatic transmission, in general, has four forward speeds and one reverse speed by a combination of a three-speed automatic transmission mechanism comprising two planetary gear units, and an over drive mechanism or an under drive mechanism having one planetary gear unit.
Transmissions having more speeds than now have been required recently to attain higher fuel efficiency and faster acceleration, etc. Under such circumstances, an automatic transmission accomplishing more than five speeds in forward by adding a three-speed sub transmission mechanism is proposed.
Said multiple speed automatic transmission comprises a torque converter and Simpson type planetary gear unit on a first axle; same type of Simpson type planetry gear unit on a second axle, so that five forward speeds are obtained.
Due to the recent trend of so-called "front engine and front drive" and varities of automobiles, an automatic transmission has been required to be small in size and to be assembled by using parts and manufacturing process in common to get more multiple speeds in mechanism.
However, certain prior art shows that in case of obtaining a six speed automatic transmission, a four speed gear mechanism has to be installed on a first axle. Due to the above, the first axle becomes long, so that installation problems particulary in "front engine and front drive" cars may occur. Also, another gear mechanism which is quite different from Simpson type has to be used. This means that parts and manufacturing prosess are not utilized in common.
Then, in the present invention, a newly designed planetary gear mechanism which can be obtained by slight modification of third and fourth speeds is used to make the size of mechanism shorter in axial direction, and to use the parts in common to cope with wide variation of automobiles: a multiple automatic transmission is obtained.